The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
There is often a requirement for mufflers intended for use with small internal combustion engines to be of compact and relatively lightweight construction. This can be particularly so for an engine of a UAV, where there are likely to be space and weight constraints within the UAV fuselage.
Further, reciprocating piston two-stroke engines can be sensitive to what is arranged on the exhaust side of the engine. More particularly, there is a need for an appropriate level of backpressure to be imposed upon the exhaust flow from a combustion chamber of a reciprocating piston two-stroke engine to inhibit escape of air/fuel mixture introduced into the combustion chamber prior to closing of an exhaust outlet port.
However, excessive backpressure can be detrimental to engine performance. In order to avoid excessive backpressure, there is often a need to prevent accumulation of deposits within a muffler on the exhaust side of such an engine, as such deposits can lead to restriction of exhaust flow through the muffler, potentially creating an undesirable level of backpressure to exhaust flow from the engine.
Reciprocating piston two-stroke engines are typically regarded as being engines which output significant noise, this noise arising from the propagation and radiation of acoustic pulses generated by the combustion process. For certain applications of such engines, including for an engine of a UAV, there may be a need for compliance with certain regulations, standards or specific user requirements regarding the level of noise emitted by the engine. Thus, there may be a need for control of engine exhaust noise through suppression of the acoustic pulses generated by the combustion process.
Accordingly, there may be various functional requirements of a muffler in order for it to be suitable for a reciprocating piston two-stroke engine of a UAV.
It is against this background that the present invention has been developed. However, it should be understood that the invention need not be limited to a muffler for a reciprocating piston two-stroke engine of a UAV. The muffler may find application in relation to other engines, including four-stroke engines. The muffler may also find application in relation to internal combustion engines for other apparatus, including for example hand-held tools such as chainsaws.